Express EL34 or 6V6

Express, Liverpool, Rocket, Dirty Little Monster, etc.

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mwelch55
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Express EL34 or 6V6

Post by mwelch55 » Mon Dec 04, 2017 9:48 pm

I noticed that some of the Trainwreck express schematics say "EL34 or 6V6" next to the power tubes. Does this require a bias adjustment when you change between EL34 and 6V6? I would think that it does, but I have never built a Trainwreck Express.

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pompeiisneaks
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Re: Express EL34 or 6V6

Post by pompeiisneaks » Mon Dec 04, 2017 10:00 pm

It would, yes, from teh sample datasheets I grabbed for them,

6V6: Plate Current Zero Signal 70mA
EL34: Plate Current Zero Signal 55mA

If it was biased for EL34, then the 6V6's woudl be fine, just a touch cold, but they could be close to shut off? The EL34's into the 6V6 may redplate.

Of course you'll need to ensure pins 1 and 8 are tied together, an amp built for 6V6's doesn't need that, but for EL34's does.

~Phil
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mwelch55
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Re: Express EL34 or 6V6

Post by mwelch55 » Tue Dec 05, 2017 4:35 pm

Thanks for the reply. So far, every amp I have built has pin 1 and 8 tied together. Is there a case where you would not want to tie 1 and 8 together?

sluckey
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Re: Express EL34 or 6V6

Post by sluckey » Tue Dec 05, 2017 4:53 pm

6V6s and 6L6s don't use pin 1. Many Fender amps have the 1500Ω grid stopper resistor mounted directly on the socket between pins 1 and 5. You can see it on this 1964 Deluxe Reverb...
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mwelch55
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Re: Express EL34 or 6V6

Post by mwelch55 » Tue Dec 05, 2017 5:55 pm

Thanks for the reply. That makes sense. It's the same as when I mount my screen resistors to pin 4 and 6 and attach B+1 to pin 6, only most if not all octal power tubes we use for amps don't use pin 6.

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Re: Express EL34 or 6V6

Post by pompeiisneaks » Tue Dec 05, 2017 7:21 pm

mwelch55 wrote:
Tue Dec 05, 2017 5:55 pm
Thanks for the reply. That makes sense. It's the same as when I mount my screen resistors to pin 4 and 6 and attach B+1 to pin 6, only most if not all octal power tubes we use for amps don't use pin 6.
If you really wanted to use those tubes in that case, though, you could install a terminal strip to move the 1.5k to it and connect there for the input, and then tie 1 to 8. This is, again, only if you want to use tubes that don't internally tie 1-8 like the EL34.

~Phil
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mwelch55
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Re: Express EL34 or 6V6

Post by mwelch55 » Tue Dec 05, 2017 10:51 pm

So far, I've built 4 amps with 1 and 8 tied together. I'll continue to do so until I find a reason not to. The only advantage I see to not connecting 1 and 8 is for the grid stopper between 1 and 5.

Mike

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